A small-form-factor may be beneficial for a mobile wireless communications device. A small-form-factor mobile wireless communications device may support relatively high spectral efficiencies, for example, 1 bit per second per Hertz (bps/Hz) or greater. Relatively high spectral efficiencies may provide improved performance in certain networking applications, such as, for example, downloading a video.
A small-form-factor mobile wireless communications device typically benefits from a waveform having a zero dB or near-zero dB peak-to-average ratio. In addition, a radio transmitter that may be included in a small-form-factor mobile wireless communications device may be peak power limited.
A lower peak-to-average ratio may allow the transmitter to operate with a higher effective radiated power at a given peak transmit power level. Thus, using a lower peak-to-average waveform, a small-form-factor mobile wireless communications device may have increased output power and thus throughput at a given range. Alternatively, a small-form-factor mobile wireless communications device using a lower peak-to-average waveform may maintain throughput at a given range with a lower peak transmit power level to provide increased battery life, and/or may allow the use of smaller and/or cheaper transmitter components.
To support higher spectral efficiencies, a small-form-factor mobile wireless communications device may consider size, weight, power, and cost implications of a receiver in addition to the transmitter. Receive signal processing requirements may often be related to the transmitted signal. For example, a receiver for processing of a non-linearly modulated continuous phase modulated (CPM) waveform may be more complex and include more components (increased size and weight, and cost) than a receiver for processing a linearly modulated waveform.
A type of high spectral efficiency modulation scheme is Nyquist-shaped quadrature amplitude modulation (QAM), which typically supports 1-3 bps/Hz using up to 5 bits per symbol and forward error correction, and typically has a 4-6 dB peak-to-average ratio. A QAM modulated waveform may use a single symbol-matched filter for demodulation, and a minimum mean squared error (MMSE) criterion non-linear decision feedback equalizer for channel equalization.
Minimum shift keying (MSK), Gaussian minimum shift keying (GMSK), and shaped offset quadrature phase shift keying are lower spectral efficiency modulation schemes that generally provide less than 1.25 bps/Hz with forward error correction, use up to 1 bit per symbol, and have a 0 dB peak-to-average ratio. An MSK waveform typically uses either a single non-pulse-matched filter and a maximum likelihood sequence estimate (MLSE) equalizer, or a single Laurent-approximation pulse matched filter and an MMSE-criterion equalizer.
Quasi-bandlimited minimum shift keying is yet another lower spectral efficiency modulation scheme that may provide less than 1 bps/Hz, 1 bit per symbol, and a 0.5 dB peak-to-average ratio. A single non-pulse-matched filter and an MLSE equalizer are typically used for demodulation.
Continuous phase modulation (CPM) is a high spectral efficiency modulation scheme that may provide up to 1-2 bps/Hz using 2 bits per symbol, and has a 0 dB peak-to-average ratio. A single non-pulse-matched filter and an MLSE equalizer are typically used for demodulation.
However, each of the above-noted modulation schemes have shortcomings. For example, QAM modulation generally requires highly-linear transmit amplification due to its large peak-to-average ratio. However, the comparatively lower peak-to-average ratio MSK and CPM modulations generally require comparatively more complicated MLSE-based demodulation. These shortcomings may result in a mobile wireless communications device being larger, heavier, more expensive, and having a shorter battery life than may be desired.
U.S. Patent Application Publication No. 2007/0002986 to Green is directed to an apparatus for representing an inherently non-linear CPM waveform as a linear pulse amplitude modulated (PAM) waveform that is the superposition of Q0≦2L-1 PAM component pulses in each symbol interval such that 95% or preferably 98% of signal energy over each symbol interval is preserved.